The invention relates to a controllable solenoid valve according to the species of the patent claims. These kinds of valves are used in such applications that intend to influence the sequence speed of cylinder controls in hydraulic drives, in particular in automatic convertible tops.
For the control of convertible top sequences, 3/2 solenoid valves are used in poppet design which are for example described in DE 3722344 A1. To prevent refluxes, an additional check valve can be installed at the pump connection or partly integrated into the solenoid seat valve, see EP 0 565 190 A1. In practical applications, weights and cinematic forces determine the movement sequences. In certain positions the own weight of the top already causes a movement. Said forces lead to unwanted high movement speeds and cause the top to slide into the end stops without being slowed-down, thus causing disturbing noise and rebounds.
In vehicles, spring or buffer elements reduce this rebound noise only in an imperfect manner. Throttles fixed in the tank adapter of the individual cylinder are known as hydraulic absorbing means. But the hydraulic throttling has several disadvantages. As the throttle effect does not change in the whole movement range, it represents a compromise; the two options are a complete rapid motion sequence and a relatively unbraked run into the end position or a completely slow motion sequence and a relatively soft rebound. Moreover, the adjustment of the hydraulic throttles is a time-consuming and labor-intensive process, because the components produced cannot be modified later. Mostly, different throttle cross sections are required within the valve connection system to get an optimum sequence. This development leads to the most expensive variant and involves the risk of mix-ups in the production process; thus, it will require more efforts. Moreover, the rigid adjustment is principally suited for one specific kind of application only; each new application requires new components.
A controllable pressure-limiting valve inserted into the tank connection of a cylinder can be used as another hydraulic solution. Thus, a counterpressure is built up which also slows down the displacement of oil out of the cylinder chamber. But in this way an additional solenoid valve is to be used which requires a corresponding space, electrical energy and trigger electronic units.